The present invention is generally directed to improved integrated wavelength division multiplexer/demultiplexer optical devices in which light of a specific wavelength (or specific wavelengths) can be added or dropped in an efficient manner. The device can be fabricated from optical polymers having a large index of refraction variation with temperature. A single filter element may be used over a wide wavelength range thereby providing for dynamic selection of wavelengths.
Devices for adding/dropping wavelength coded signals (light of a specific wavelength or wavelengths) are known in the art as disclosed in D. C. Johnson, K. O. Hill, F. Bilodeau, and S. Faucher, xe2x80x9cNew Design Concept For A Narrowband Wavelength-Selective Optical Tap And Combiner,xe2x80x9d Electron Lett., Vol. 23, pp. 668-669 (1987) and C. R. Giles and V. Mizrahi, xe2x80x9cLow-Loss Add/Drop Multiplexers For WDM Lightwave Networks,xe2x80x9d Proc. 100C, pp. 66-67 (1995), incorporated herein by reference. Such devices employ optical fibers which are utilized predominantly in telecommunication systems in addition to local area networks, computer networks and the like. The optical fibers are capable of carrying large amounts of information and it is the purpose of devices of the present invention to extract/inject a selected amount of information from/onto the fiber by segregating the information carried on different wavelength channels.
Devices of this type are comprised of a variety of components which together provide the desired segregation of wavelength coded signals. Integrated optical couplers and especially directional couplers have been developed to accomplish evanescent directional coupling as disclosed in E. A. J. Marcatili, xe2x80x9cDielectric Rectangular Waveguide And Directional Couplers For Integrated Optics,xe2x80x9d Bell Syst. Tech. J., p. 2071 (1969), incorporated herein by reference. Optical signals are coupled from one planar waveguide to another. The signals in the second planar waveguide propagate in the same direction in which the signals travel in the first planar waveguide.
MMI (multimode interference) couplers have been developed to accomplish coupling as disclosed in L. B. Soldano and E. C. M. Pennings, xe2x80x9cOptical Multi-Mode Interference Devices Based On Self-Imaging: Principles And Applications,xe2x80x9d J. Lightwave Technol., Vol.13, pp. 615-627 (1995), incorporated herein by reference. MMI couplers achieve self-imaging whereby a field profile input into a multimode waveguide is reproduced in single or multiple images at periodic intervals along the propagation direction of the guide.
Optical circulators are optical coupling devices that have at least three ports. Three-port circulators couple light entering port 1 to port 2, light entering port 2 to port 3, and light entering port 3 to port 1.
Diffraction gratings (e.g. Bragg gratings) are used to isolate a narrow band of wavelengths as disclosed in K. O. Hill and G. Meltz, xe2x80x9cFiber Bragg Grating Technology Fundamentals And Overview,xe2x80x9d J. Lightwave Technol. Vol. 15, pp.1263-1276 (1997) and T. Erdogan, xe2x80x9cFiber Granting Spectra,xe2x80x9d J. Lightwave Technol., Vol. 15, pp. 1277-1294 (1997), incorporated herein by reference. Such grating reflectors have made it possible to construct a device for use in adding or dropping a light signal at a predetermined center wavelength to or from a fiber optic transmission system without disturbing other signals at other wavelengths as disclosed in L. Eldada, S. Yin, C. Poga, C. Glass, R. Blomquist, and R. A. Norwood, xe2x80x9cIntegrated Multi-Channel OADM""s Using Polymer Bragg Grating MZI""s,xe2x80x9d Photonics Technol. Lett., Vol. 10, pp. 1416-1418 (1998), incorporated herein by reference.
It would be desirable to be able to drop a wavelength with more precision than current devices within a dynamic range of wavelengths for a single optical signal device rather than employing multiple optical signal devices for the same purpose.
The present invention is generally to optical signal devices having fine tuning means which provide for the more efficient control of the wavelength of light which is to be segregated from a multiple wavelength light signal.
The optical signal device of the present invention has a unique array of materials and also includes altering the temperature of the optical signal device which provides for the precise selection of a targeted wavelength for dropping or adding an optical signal and which provides for the rapid change of wavelengths from one targeted wavelength to another.
In particular the optical signal device of the present invention comprises:
a) a substrate;
b) a pair of spaced apart cladding layers comprised of materials having at least similar refractive index values;
c) a core layer including a waveguide or a pair of opposed waveguides positioned between the pair of cladding layers having a refractive index value greater than the refractive index value of the cladding layers such that the difference between refractive index values of the core layer and cladding layers enables a multiple wavelength light signal to pass through the device in a single mode;
d) a grating forming a filter means for causing a single wavelength of light of said multiple wavelength light signal to be segregated therefrom; and
e) means for varying the refractive index of at least the core layer to control the wavelength of the light which is to be segregated from the multiple wavelength light signal.
In a preferred construction of the optical signal device at least the core layer is made of a thermosensitive material and the means for varying the refractive index is by heating the thermosensitive material. The thermo-optic effect, being the preferred refractive index tuning effect, is used as the illustrative effect throughout most of this disclosure. But generally, any refractive index tuning effect (e.g., electro-optic effect, stress-optic effect) and any combination thereof can be used in the present invention to vary the refractive index.
In a preferred construction of the optical signal device there are two cladding layers positioned between the refractive index varying means and the core with each of the two cladding layers having a different refractive index. Methods of fabricating the optical signal devices of the present invention are also disclosed.